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Oracle Tips by Burleson Consulting
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Oracle PGA memory
allocation for dedicated connections
When a dedicated connection is made to Oracle, an isolated memory
region called the program Global Area is allocated in UNIX RAM
memory. The PGA consists of the following components:
* Sort area – This is the largest and most important area of the PGA
* Session information – This small area contains internal address
for the connection to allow the connection to communicate with
Oracle.
* Cursor state – This component of the PGA contains all reentrant
values for the executing connection.
* Stack space – This area contains miscellaneous control structures.
The largest component of a PGA is the sort area size, and Oracle
allows you to dynamically change the sort area size at the session
level.
alter session set sort_area_size=10m
deferred;
When you issue this alter session command, you instruct UNIX to
expand the sort area within the PGA at the time that the sort is
required. To illustrate the deferred RAM memory allocation in UNIX.
Here we see that Oracle interfaces with UNIX to issue the malloc()
command to provide a RAM sort area. This RAM region is only
allocated after the retrieval from the database has been completed,
and the memory only exists for the duration that the sort is
required. This technique reduces the RAM memory demands on the UNIX
server and ensures that the RAM is only available when it is needed
by Oracle.
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